1. Field of the Invention
This invention relates to imaging systems using a sensor element to control the emission of at least some of the light of one or more light-emitting sources. In particular, this invention is directed to architectures, characteristics and methods of integration of a light sensor configuration with different light sources, using micro-fabricated metal spring contacts.
2. Technical Background
Image printbars which are used in imaging systems are well known in the art. Such printbars are generally comprised of a linear array of a plurality of discreet, light-emitting sources. Examples of such printbars include light-emitting diodes and lasers. A method of forming lasers in semiconductor material, which may be used in the formation of laser printbars has been taught by, for example, U.S. Pat. No. 5, 978, 408 to Thornton, entitled, xe2x80x9cHighly Compact Vertical Cavity Surface Emitting Lasersxe2x80x9d, issued Nov. 2, 1999; and U.S. Pat. No. 5,843,802 to Beernink, et al., entitled, xe2x80x9cSemiconductor Laser Formed by Layer Intermixingxe2x80x9d, issued Dec. 1, 1998, both commonly assigned and hereby incorporated by reference.
In a typical printbar arrangement, a large number of individual light-emitting sources are arranged in an elongated, planer array that is placed adjacent an image recording member. By providing relative motion between the printbar and the image recording member, the printbar scans the image recording member, and by selectively illuminating the individual light-emitting sources, a desired light image is recorded on the image recording member.
The selective illumination of the individual light-emitting sources is performed according to image-defining data that is applied to printbar driver circuitry. Conventionally, the image-defining data takes the form of simple binary video data signals. Those data signals may be from any of a number of data sources such as a Raster Input Scanner (RIS), a computer, a word processor, or a facsimile machine. Typically, the binary video data is clocked into a shift register. After completely shifting the data into the shift register, the contents of the shift register is transferred in parallel into latch circuits for temporary storage. Then, upon the occurrence of a start of a line signal, the latch data is applied to the printbar drive circuit which thereby illuminates the individual light-emitting sources of the printbar so as to produce a line of the latent image. A complete latent image is formed by performing successive line exposures until the image is produced.
Due to their narrow beam profile and high efficiency, photolithographically configured laser printbars have been found to provide certain advantages. Proposed laser printbars consist of an array of Vertical-Cavity Surface-Emitting Lasers (VCSELs) which may be designed with as small as 3 xcexcm pitch. At such a pitch, a 4 cm-long laser chip would accommodate more than 13,300 individually addressable laser elements, more than necessary for 1,200 dpi printing on a standard 11-inch-long paper, where 13,200 elements are required. A drawback of such a large number or light sources, ultra-high density-packed, is the expectation of non-uniformity of laser responses. This non-uniformity has the potential for high spatial frequency that makes the effect on printed images noticeable to the human eye.
One manner of addressing non-uniformity is to perform a calibration when the printbar is being manufactured. A problem with this process is that it does not address aging of the lasers, fluctuations in driver chip operation or environmental variations such as temperature and humidity, among others.
A second proposal is to form a sensor or detector as part of the printbar in order to perform periodic calibrations during the lifetime of the printbar. This concept is described in U.S. Pat. Ser. No. 08/921,942, entitled, Semiconductor Laser With Integrated Detector Structure, Thornton et al., filed Aug. 27, 1997. A drawback with this proposal is the complexity of forming the device.
Similar issues may be present in many other imaging systems where one or more light-emitting sources need to be controlled in order to address issues like intrinsic non-uniformity, drift of characteristics or differential aging.
Therefore, it has been considered desirable to provide an apparatus and method to integrate a sensor element in a hybrid structure with a printbar or another compatible light-emitting source using simple patterned micro-spring metal contacts.
Provided is a hybrid structure or device integrated in a substrate, where in some cases the substrate is substantially transparent to light at infrared wavelengths. Integrated on the substrate are a plurality of micro-spring interconnects, where the micro-spring interconnects are formed of an elastic material that is initially fixed to a surface on the substrate. Upon release of a sacrificial layer a free portion moves out of the plane of the substrate in a self-assembling manner. A sensor is formed on the same substrate, and includes an active layer and contacts. The active layer may be substantially transparent to light at infrared wavelengths. The micro-spring interconnects and the sensor are integrated on the substrate and configured using a compatible manufacturing process.
With attention to a further embodiment of the present invention, a light-emitting source is provided which may be an array of individual light-emitting sources. The light sources may be lasers such as, Vertical Cavity, Surface-Emitting Lasers (VCSELs), which are formed on the substrate, and the VCSELs are capable of emitting light at an infrared wavelength. Other light sources may also be used such as an array of light emitting diodes (LEDs). The substrate holding the spring contacts and sensor, and the substrate including the light sources are aligned such that at least a portion of the light emitted by the light source is directed through the second substrate and the sensor which may be, substantially transparent at infrared wavelengths.
Separate embodiments describe similar integration schemes for less directional light-sources, such as Light-Emitting Diodes (LEDs). It is to be appreciated that the light of other wavelengths may be used in conjunction with the concepts of this invention.